Heat for a few seconds (3)
I believe the answer is:
zap
'heat for a few seconds' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for zap that I've seen before include "Destroy, obliterate" , "Kill or shoot (in a microwave oven?)" , "Keep changing TV channels" , "Hit (colloq.)" , "Attack" .)